Various types of auxiliary drives for vehicles such as bicycles are known in the patent literature. Representative of the art are the following patents:
U.S. Pat. No. 1,259,989 describes a gasoline engine driven auxiliary drive which includes two driven rollers which engage opposite sides of the rim of the back wheel of a bicycle.
U.S. Pat. No. 2,031,881 describes a motor bicycle including a gasoline engine driven roller which engages the outer surface of the back tire of the bicycle.
U.S. Pat. No. 2,069,679 describes a gasoline engine driven auxiliary drive which includes a geared member which engages a suitably configured tooth containing tire tread of a bicycle.
U.S. Pat. No. 3,339,659 describes a powered friction-driving device for vehicles including a pair of frusto-conical rollers which simultaneously engage the vehicle wheel. Speed shifting apparatus is provided for altering the point or line of engagement of the drive members with the tire such that the speed of the wheel may be changed for a given speed of rotation of the drive members.
U.S. Pat. No. 3,891,044 provides a cone shaped electric motor driven friction drive which engages an auxiliary rim associated with the front wheel of a bicycle.
U.S. Pat. No. 3,915,250 describes an auxiliary drive for a bicycle employing a pair of rollers which pinch the back time of a bicycle therebetween.
U.S. Pat. No. 4,143,730 describes an electric motor driven friction drive which engages the outer surface of the back tire of a bicycle.